In which case is heat involved: mixing 100.0-g samples of 90'C water and 80'C water or mixing 100.0-g samples of 60'C water? assume no heat is lost to the environment.

Question

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Answer 1

Mixing 100 g sample of the same T has no heat exchange.
Mixing two different temperataures has a heat exchange. One gets warmer; the other gets cooler.